//给定两个整数数组 inorder 和 postorder ，其中 inorder 是二叉树的中序遍历， postorder 是同一棵树的后序遍历，请你构造并
//返回这颗 二叉树 。 
//
// 
//
// 示例 1: 
// 
// 
//输入：inorder = [9,3,15,20,7], postorder = [9,15,7,20,3]
//输出：[3,9,20,null,null,15,7]
// 
//
// 示例 2: 
//
// 
//输入：inorder = [-1], postorder = [-1]
//输出：[-1]
// 
//
// 
//
// 提示: 
//
// 
// 1 <= inorder.length <= 3000 
// postorder.length == inorder.length 
// -3000 <= inorder[i], postorder[i] <= 3000 
// inorder 和 postorder 都由 不同 的值组成 
// postorder 中每一个值都在 inorder 中 
// inorder 保证是树的中序遍历 
// postorder 保证是树的后序遍历 
// 
//
// Related Topics 树 数组 哈希表 分治 二叉树 👍 1044 👎 0


package leetcode.editor.cn;

// [106]从中序与后序遍历序列构造二叉树

import java.util.HashMap;

public class ConstructBinaryTreeFromInorderAndPostorderTraversal_106 {
    private class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode() {
        }

        TreeNode(int val) {
            this.val = val;
        }

        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }

    public static void main(String[] args) {
        Solution solution = new ConstructBinaryTreeFromInorderAndPostorderTraversal_106().new Solution();
        solution.buildTree(new int[]{9, 3, 15, 20, 7}, new int[]{9, 15, 7, 20, 3});
    }
    //leetcode submit region begin(Prohibit modification and deletion)

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     * int val;
     * TreeNode left;
     * TreeNode right;
     * TreeNode() {}
     * TreeNode(int val) { this.val = val; }
     * TreeNode(int val, TreeNode left, TreeNode right) {
     * this.val = val;
     * this.left = left;
     * this.right = right;
     * }
     * }
     */
    class Solution {
        int[] inorder;
        int[] postorder;
        HashMap<Integer, Integer> map;

        public TreeNode buildTree(int[] inorder, int[] postorder) {
            map = new HashMap<>(inorder.length);
            for (int i = 0; i < inorder.length; i++) {
                map.put(inorder[i], i);
            }
            this.inorder = inorder;
            this.postorder = postorder;
            return getTree(0, postorder.length - 1, 0, postorder.length - 1);
        }

        private TreeNode getTree(int li, int ri, int lp, int rp) {
            if (lp > rp) {
                return null;
            }
            TreeNode node = new TreeNode(postorder[rp]);
            int index = map.get(postorder[rp]);
            node.left = getTree(li, index - 1, lp, lp + index - li - 1);
            node.right = getTree(index + 1, ri, lp + index - li, rp - 1);
            return node;
        }
    }
//leetcode submit region end(Prohibit modification and deletion)

}